1. Field of the Invention
The present invention generally relates to technology of structuring an audio-transmission system based on object data for drawing pictures of a virtual three-dimensional space on a screen, and simulating audio signals pursuant to such audio-transmission system. Particularly, this invention relates to technology of performing simplified operations of audio simulation.
2. Description of the Related Art
In game devices, songs or voices are output in correspondence with scenes together with the motion picture displayed on the screen in order to enhance the ambience. For example, a virtual game space is formed by arranging various objects or virtual characters (objects) in a virtual space composed of three-dimensional coordinates and, upon a main character of the game freely moving in the game space and progressing in the game, music is played as background music in correspondence with such scenes. Further, car race games are structured to generate sounds of engines, skidding, collisions, etc. in correspondence with the game progress. Thus, to the program storing the game story, further stored in advance are audio signals outputs of, for example, music, voices, and sound effects corresponding to the screen to be displayed in accordance with the game progress. The block diagram of conventional game device hardware having such a function is shown in FIG. 33.
The game device shown in FIG. 33 comprises a main CPU 1, memory 2, sound processor 3, CG drawing unit 4, display 5, speakers 6a and 6b, and I/O interface 7. The I/O interface 7 includes a CD-ROM cartridge interface for interfacing with recording mediums such as a CD-ROM, and interface of input devices such as control pads. Game program data provided from mediums such as a CD-ROM is supplied to the memory 2 via the I/O interface 7, object data (i.e., coordinate data and shape data of polygons) is supplied to the CG drawing unit 4, and sound data (song data and waveform data arranged as audio for background music or engine sounds of cars) and sound control data such as MIDI formats are supplied to the sound processor 3. The CG drawing unit 4 includes a frame buffer, color RAM, encoder, etc., and represents objects displayed on the display 5 as polygons (three-dimensional figures composed of apexes and ridgelines defined in a model coordinate system) pursuant to command data supplied from the main CPU 1. The CG drawing unit 4 further displays this on the display 5 upon performing modeling conversion to a world coordinate system, visual field conversion to a prescribed camera viewpoint, three-dimensional clipping processing, hidden line processing, texture mapping processing, shading processing, display priority processing, and so forth.
The sound processor 3 includes the likes of a sound memory, sound CPU, and D/A converter for conversion to two-channel audio signals. Identification (ID) information and sound data corresponding to sound source types are associated and registered to the sound memory. The sound CPU reads out sound data from the sound memory based on ID information of the sound source designated by the main CPU 1, realizes special sound effects such as an echo, reverb, chorus, etc. based on the DSP function, and outputs audio signals to the speakers 6a and 6b. The main CPU 1 interprets game program commands corresponding to input operations from input devices such as controller pads operated by a player, and performs prescribed image processing and audio processing. For example, upon performing audio processing while displaying images of a scene wherein a car is travelling along a bumpy road in a virtual three-dimensional space, the following processing is performed. Supplied from the main CPU 1 to the CG drawing unit 4 is command data relating to the drawing of objects (cars), and supplied from the main CPU 1 to the sound CPU is ID information predetermined in accordance with the sound source type (skidding sound, engine sound, etc.). This ID information is priorly stored in the program according to game scenes (e.g., a sound source for generating driving sounds is designated if it is a driving scene of a car), or, is used for sound processing (e.g., for designating collision sounds of cars) according to the type of prescribed event (e.g., collision) which occurs to an object. The sound CPU reads the registered sound data associated with ID information from the sound memory and outputs this to the speakers 6a and 6b. 
The audio processing realized in the aforementioned conventional art, however, gives no consideration to the relationship of the sound source position and the listening position (sound-receiving point) on the screen, and merely reads sound data from the sound memory and outputs this to the speakers. In other words, no consideration is given to the panning of sound images or the level of volume. Further, no consideration is given to the sound generated from the sound source being influenced by objects such as walls arranged in the three-dimensional space; for example, influence from shielding or reflection, or reflection coefficients characteristic to such object. It was therefor not possible to realize so-called 3D sounds based on the actual environment. That is, although in reality the distance between the sound source position and the listening position (sound-receiving point) and the reflective states of sound continuously change temporally, a prescribed sound was expressed with several or a single representative sound source. For example, when a car drives through a tunnel, the same sound was generated without giving consideration to the vehicle type, travelling speed thereof, or the size, shape, length, etc. of the tunnel. Similarly, no consideration was given at all to the reflected sound from the tunnel or the driving sound and the like of other cars. Moreover, unnaturalness was caused due to the driving sound of cars being the same in the city as well as along the coastline.
Nevertheless, complex and difficult operations would be necessary for setting an audio transmission system in the virtual three-dimensional space and precisely simulating the sound generated from the sound source object at the sound-receiving point. For instance, audio signals have surface acoustic waves, the medium thereof being solid, liquid, gas, and create various audio phenomena by emission, transmission, absorption, refraction, diffraction, interference, dispersion, scattering, or diffusion in forms of surface waves, spherical waves, standing waves, progressive waves, etc. The analysis of sound fields is conducted with a wave equation, finite boundary element method, and so on, and generally requires vast operational loads and is not adequate for complex sound fields. Especially, such as in games, when the virtual three-dimensional space environment changes momentarily in accordance with the game progress and the propagation characteristics of sounds composing the sound transmission system change in real time; for example, when scenes change temporally and continuously such as a sound-generating object gradually approaching and retreating from the listening position, desired is audio simulation pursuant to simplified operations.